Various pressure washers are known for pumping fluid, particularly water, at a high pressure. Such pressure washers use various pump arrangements for delivering the water, and typically another fluid, such as detergent, from an external source to a spray nozzle. Some known pressure washers such as those described in Paige, U.S. Pat. No. 5,067,654 and Paige, U.S. Pat. No. 5,086,975, both assigned to the assignee of the instant application, include a pump housing having an inlet conduit for the delivery of fluid drawn from a source, an outlet conduit for delivery of fluid to a dispensing spray nozzle and at least one, and more particularly a plurality of pumping chambers connected in parallel across the inlet and outlet conduits. The spray nozzle from the outlet conduit has a valve which is selectively opened for permitting the outflow of pumped fluid or closed for blocking fluid outflow. Such a pressure washer includes means for recirculating the flow of fluid through the pump when the spray nozzle valve is closed.
Each of the pumping chambers includes a pumping piston which reciprocates within the chamber. Input check valves are located in input conduits disposed between the inlet conduit of the pump and each pumping chamber and are normally biased in a closed position. Each input check valve is opened as the pressure in a respective pumping chamber is reduced, thereby permitting fluid to enter the pumping chamber from the inlet conduit. Output check valves are located in output conduits between each pumping chamber and the outlet conduit of the pump and are also normally biased in a closed position. Each output check valve is opened when the pressure in a respective pumping chamber increases, thereby expelling fluid from the pumping chamber through the output conduit and into the outlet conduit of the pump.
The input and output check valves are mounted in valve guides each having an outer cylindrical surface adapted to be tightly received within valve guide bores disposed in the pump housing. During operation, considerable stress is placed upon the input and output valves and valve guides as the pistons reciprocate within the pumping chambers. As a result, a frictional fit between the valve guides and the guide bores is often not sufficient to securely retain the valves within the pump housing. In the past, the valve guides were secured within the guide bores by ultrasonically welding a cap or plug located outside of the guides to the pump housing. Although ultrasonic welding usually provides an adequate attachment means between the valve guides and the pump housing, it is somewhat unreliable. Also, ultrasonic welding of each individual valve guide to the pump housing is a time consuming process.